Bump skiboot to 5.1.12, to current master for garrison

Since Garrison is building from skiboot master rather than 5.1.x
stable branch during bringup, since the libgcc dependency removal
patch was merged into skiboot stable (and master) we don't need
it in op-build anymore and we need to bump garrison skiboot to
continue to build.

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
3 files changed